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Physics > CP9 > Flashcards

CP9 Flashcards

1
Q

How does the atomic structure of a metal make it a conductor of electricity?

A

There are very few electrons in the outer shell that are weakly attracted to the nucleus. These electrons can easily be removed, so the wire has many ‘free’ electrons.

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2
Q

Where do electrons move to in a battery?

A

Electrons are negatively charged, so they move towards the positive terminal of the battery.

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3
Q

What are the circuit symbols?

A
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4
Q

What is the difference between the conventional direction of current flow and the direction of electron flow?

A

Direction of electron flow: Move to the positive terminal of the battery
Conventional direction of current flow: Move from the positive terminal to the negative terminal of the battery

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5
Q

What is a series circuit?

A

A circuit where there is just one route the current can take around the circuit (all the lamps in the circuit are on the same line)

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6
Q

What is a parallel circuit?

A

A circuit where there are junctions that allow the current to take different routes (the lamps are on different lines which are parallel to each other)

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7
Q

What is the difference between series and parallel circuits in terms of lamps?

A

In series circuits, lamps cannot be switched on and off individually, and if one lamp fails they will all switch off. In parallel circuits, each lamp can be switched separately.

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8
Q

What units are electric currents measured in?

A

Amps (A).

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9
Q

What is used to measure electric currents

A

An ammeter.

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10
Q

How is an ammeter used?

A

An ammeter is connected in series to measure the current passing through a component or circuit.

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11
Q

Why is the total amount of current the same all around the circuit?

A

As current is conserved. The amount of current leaving the positive terminal is the same as the current arriving at the negative terminal.

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12
Q

What direction does the current flow in proportion to electrons?

A

Electrons flow from the negative terminal to the positive terminal, and current is the opposite, therefore current always flows from the positive terminal to the negative terminal.

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13
Q

What is potential difference

A

The difference in energy carried by electrons before and after they have flowed through a component.

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14
Q

What is potential difference also known as?

A

Voltage.

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15
Q

What is a component?

A

A part of something (a lamp is a component of an electrical circuit)

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16
Q

What does a current need to move around a circuit?

A

A potential difference. For the current to flow, the circuit must be closed and contain a source of potential difference (such as a cell or battery). The electrons all move together when a current flows.

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17
Q

How does the amount of potential difference affect the amount of current?

A

The bigger the potential difference across a component, the bigger the current.

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17
Q

How does the amount of potential difference affect the amount of current?

A

The bigger the potential difference across a component, the bigger the current.

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18
Q

What unit is potential difference measured in?

A

Volts (V).

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19
Q

What is used to measure potential difference?

A

A voltometer.

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20
Q

What is electric charge measured in?

A

Coulombs (C).

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21
Q

What is electric current?

A

The rate of flow of charge.

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22
Q

What is the equation for charge?

A

Charge(C)=Current(A) x Time(s)

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23
Q

What is the symbol equation for charge?

A

Q=l x t (Q=Charge, l=current, t=time)

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24
Q

What is the formula triangle for charge?

A

Charge
Current | Time

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25
Q

How is energy transferred in a circuit?

A
  1. A cell contains a store of energy.
  2. Energy is transferred to the charge.
  3. The charge can now transfer energy to the components in the circuit. It has potential energy.
  4. Energy is transferred from the charge as it moves through the lamp
  5. The lamp transfers energy to the surroundings by heating and by light.
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26
Q

What is the potential difference of a cell?

A

The amount of potential energy the cell transfers to each coulomb of charge flowing through it (e.g. There is a potential difference of 1 volt when there is a transfer of one joule of energy to each coulomb of charge).

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27
Q

What is the equation for energy transferred?

A

Energy transferred(J)=Charge moved(C) x Potential difference(V)

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28
Q

What is the word equation for energy transferred?

A

E=Q x V (E=Energy transferred, Q=Charge, V=Potential difference)

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29
Q

Why do some wires need a larger potential difference than others to produce a current?

A

As they have a large electrical resistance.

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30
Q

What is electrical resistance?

A

A way of saying how difficult it is for electricity to flow through something.

31
Q

What unit is resistance measured in?

A

Ohms(Ω).

32
Q

What is the equation for potential difference (involving resistance)?

A

Potential difference(V)=Current(A) x Resistance(Ω)

33
Q

What is the word equation for potential difference (involving resistance)?

A

V=l x R (V=Potential difference, l=Current, R=Resistance)

34
Q

What is the formula triangle for potential difference (involving resistance)?

A

Potential difference
Current | Resistance

35
Q

What happens when a resistor is connected in series?

A

The total resistance of the circuit is increased because the pathway becomes harder for current to flow through.

36
Q

How does the amount of potential difference correlate to the number of resistors?

A

The potential difference from a cell is shared between the resistors, but it may not be shared equally. There will be greater potential difference across resistors with higher resistances.

37
Q

What happens when a resistor is connected in parallel?

A

The total resistance of the circuit is less than the resistance of the individual resistors. This is because there are now more paths for the current.

38
Q

What variable is in direct proportion with potential difference across a fixed resistor?

A

Current (e.g. The more the potential difference, the more the current)

39
Q

What is a diode?

A

A component that only allows current to flow in one direction. This is because there is low resistance if the potential difference is in one direction but a very high resistance if the potential difference is in the opposite direction.

40
Q

What does a potential difference across a filament lamp cause it to do?

A

It causes a current to flow through it. The current causes the filament to heat up and glow. The greater the potential difference, the more current flows and the hotter and whiter the filament gets.

41
Q

What happens to a filament lamp after it heats up and what does this mean for the proportion of potential difference to charge?

A

Its resistance increases. This means that when the potential difference changes, the current does not change by the same percentage (the two variable are not in direct proportion)

42
Q

How does resistance change in a light dependent resistor (LDR)?

A

It has a high resistance in the dark but the resistance gets smaller when the light intensity increases.

43
Q

How does resistance change in a thermistor?

A

They have high resistances at low temperatures but as the temperature increases the resistance decreases.

44
Q

How does the amount of ions inside a resistor correlate with resistance?

A

The more ions there are, the more likely it is that electrons will collide with them. The more collisions they make with the ions, the harder it is for them to pass through, so the higher the electrical resistance.

45
Q

How can resistance in circuits be reduced?

A
  1. By using wires made out of metals with low resistance, such as copper.
  2. By using thicker wires also have lower resistance as it reduces the chances of electrons bumping into ions.
  3. By cooling metals so that the lattice ions are not vibrating as much.
46
Q

What is the formula for energy transferred (involving current)?

A

Energy transferred(J)=Current(A) x Potential difference(V) x Time(s)

47
Q

What is the word equation for energy transferred (involving current)?

A

E=l x V x t (E=Energy transferred, l=Current, V=Potential difference, t=Time)

48
Q

What is the formula triangle for energy transferred (involving current)?

A

Energy transferred
Current | Potential difference | Time

49
Q

What is power?

A

The amount of energy transferred per second.

50
Q

How is power shown on appliances?

A

It is often shown on appliances as the ‘Power rating’.

51
Q

What unit is power measured in?

A

Watts(W).

52
Q

What is the equation for power?

A

Power(W) = Energy transferred(J) / Time taken(s)

53
Q

What is the symbol equation for power?

A

P=E / t (P=Power, E=Energy transferred, t=Time taken)

54
Q

What is the equation for electrical power involving current but no resistance?

A

Electrical power(W) = Current(A) x Potential difference(V)

55
Q

What is the symbol equation for electrical power involving current but no resistance?

A

P = l x V (P=Power, l=Current, V=Voltage)

56
Q

What is the equation for electrical power involving current and resistance?

A

Electrical power(W) = Current²(A²) x Resistance(Ω)

57
Q

What is the symbol equation for electrical power involving current and resistance?

A

P = l² x R (P=Power, l=Current, R=Resistance)

58
Q

What is the national grid?

A

The system of wires and transformers that distributes electricity around the country.

59
Q

What is a direct current (d.c.)?

A

When the direction of the movement of charge stays the same.

60
Q

How is mains electricity produced?

A

Using generators that rotate, causing the direction of the current to keep changing. This creates an alternating current (a.c.).

61
Q

What is mains electricity?

A

The electricity supply from power stations to households.

62
Q

What is an alternating current (a.c.)?

A

When the direction of the current changes many times each second.

63
Q

What is the power rating of domestic appliances measured in?

A

Watts(W).

64
Q

How many joules of energy would a kettle transfer per second with a power rating of 3kW?

A

3000 joules per second is transferred from the mains electricity supply to a store of thermal energy in the water.

65
Q

What features does a 3-pin plug have to safely connect appliances to mains electricity?

A
  1. Earth wire
  2. Neutral wire
  3. Fuse
  4. Live wire
66
Q

What is Earth Wire?

A

Earth wire is a wire that connects the metal parts of the appliance to a large metal spike or metal tubing that is pushed into the ground.

67
Q

What is Neutral wire?

A

Neutral wire is a wire that is the return path to the power station.

68
Q

What is a fuse?

A

A safety device that is a tube with a wire inside. It is marked with the current it can carry. Usually 3A, 5A or 13A.

69
Q

What is Live wire?

A

Live wire is a wire that connects the appliance to the generators at the power station.

70
Q

What happens when a switch is off?

A

No current goes through the appliance.

71
Q

What happens to a wire when a current passes through it?

A

This makes the wire get hotter. If the current exceeds a certain value, the wire melts. This breaks the circuit and stops the current.

72
Q

What does having a fuse in place prevent?

A

A fuse prevents an appliance from drawing too much current, causing overheating either in the wall or in the appliance which can cause fires.

73
Q

Why is the metal part of appliances connected with earth wire?

A

As if you touched metal, you might get a dangerous electric shock. The current would flow through you into the ground. Using earth wire means that the current goes into the ground instead of through you.

74
Q

What are circuit breakers?

A

They are alternatives to fuses that work by detecting a change in the current and then safely switching off the supply.

75
Q

What are some advantages to circuit breakers over fuses?

A
  1. Once the fault is fixed, they can be switched back on again, whereas a fuse has to be replaced.
  2. They work very quickly, so can save lives whereas a fuse takes some time to melt and will not prevent you from getting shock if you touch the live wire.

Physics (13 decks)

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